Evaluation of RADARSAT Standard Beam data for identification of potato andrice crops in India

The Canadian satellite RADARSAT launched in November 1995 acquires C-band N H polarisation Synthetic Aperture Radar (SAR) data in various incident angl es and spatial resolutions. Tn this study, the Standard Beam S7 SAR data wi th 45 degrees-49 degrees incidence angle has been used to discriminate rice and potato crops grown in the Gangetic plains of West Bengal state. Four-d ale data acquired in the 24-day repeat cycle between January 2 and March 15 , 1997 was used to study the temporal backscatter characteristics of these crops in relation to the growth stages. Two, three and four-date data were used to classify the crops. The results show that the backscatter was the l owest during puddling of rice fields and increased as the crop growth progr essed. The backscatter during this period changed from -18 dB to -8 dB. Thi s temporal behaviour was similar to that observed in case of ERS-SAR data. The classification accuracy of rice areas was 94% using four-date data. Two -date data, one corresponding to pre-field preparation and the other corres ponding to transplantation stage, resulted in 92%; accuracy. The last obser vation is of particular interest as one may estimate the crop area as early as within 20-30 days of transplantation. Such an early estimate is not fea sible using optical remote sensing data or ERS-SAR data. The backscatter of potato crop varied from -9 dB to -6 dB during the growth phase and showed large variations during early vegetative stage. Two-date data, one acquired during 40-45 days of planting and another at maturing stage, resulted in 9 3% classification accuracy for potato. All other combinations of two-date d ata resulted in less than 90% classification accuracy for potato. (C) 1999 Elsevier Science B.V. All rights reserved.